For years, harvesting pumas has been used as a way to maintain robust mule deer populations for hunters to target. Now, a new Panthera study suggests that heavy hunting of pumas may actually have the opposite effect. This blog explores the science behind pumas and their prey, and how that science may, or may not, influence policy decisions. Consider these three key points:

A puma’s age may be the primary factor that determines which prey they prefer. Our research shows that older cats prefer larger prey like elk, while younger cats specialize on mule deer.

Heavy hunting of puma populations does not always reduce the number of pumas, but instead tends to lower the average age of the population.

Lowering the age of pumas in a population may actually increase impacts on mule deer, contradicting the original goal of hunting pumas to aid mule deer in the first place.

One of the established rationales for legally hunting pumas in North America is to increase populations of prey animals such as deer and elk for hunters to target, even though the science on its effectiveness is mixed. On the surface, it makes sense to think that killing pumas will result in more mule deer. Eliminate the predator and the prey should flourish! Ecology, however, isn’t that simple. In a new paper just published in the open-access Conservation Biology Society journal, Conservation Science and Practice, we offer a provocative twist on this age old paradigm. What if hunting pumas to help mule deer is actually hurting deer populations instead?

We’ve known for decades that pumas have little influence on deer populations (this was among the key findings of Maurice Hornocker’s landmark work on pumas in central Idaho in the 1960s). However, under pressure from skeptical sportsmen who are concerned over future hunting opportunities, some biologists keep trying to prove otherwise, asking the same questions year-after-year about pumas affecting prey abundance. In another long-term experiment from Idaho, researchers actively removed pumas and coyotes to see if they could increase deer numbers. Removing pumas did allow more fawns to survive longer intervals, and did increase the number of does with fawns in the population. However, in the end, these differences did not translate into deer population growth.

What new information do we have to add to this contentious issue? We have been trying to decipher why all pumas don’t eat the same prey in our small population in northwest Wyoming. What we found was startling in its simplicity. Puma age was the primary difference between foraging groups in our study area; the older the cat, the larger the prey it specialized upon. For example, two-year old pumas specialized on deer, while adult cats of more than five years specialized on elk.

Previous research has shown that heavy puma hunting generally does not reduce the number of pumas in a landscape. Rather, it tends to reduce the average age of pumas in the population instead. This is because hunters target older, larger pumas, which once removed, are replaced by younger cats migrating in to take over vacant territories. Since younger cats specialize on deer, rather than elk, heavily hunted populations of pumas may put more pressure on deer populations than an un-hunted population with a higher average cat age. We believe that this is a provocative finding worthy of further investigation by the scientific community.

This graph shows the relationship between a puma's age and their prey preference.

Biologists agree that weather and food are the primary driving forces that influence deer numbers, and others ungulates as well. For example, it is widespread and prolonged droughts that are considered the primary cause of the decline of Rocky Mountain mule deer, not predators. Despite these facts, efforts to remove pumas to aid deer populations persist throughout the American West. Colorado Parks and Wildlife recently launched a controversial plan hiring contract hunters and trappers to remove bears and pumas to aid ailing mule deer populations. The proposal was met with scientific and public criticism, but moved forward anyway due to pressure from hunting groups.

Ensuring a future for pumas in North America is now mostly an issue of habitat protection and increasing human tolerance for large predators. However, it is also important that the best science informs wildlife policy. We encourage rigorous research and greater transparency by wildlife agencies to better determine the effects of puma hunting on deer and elk populations, even those unexpected and unintentional effects that may occur as we have highlighted here. This will promote more effective puma, deer and elk conservation, and greater inclusivity of all people in wildlife conservation and management.